The present application is a continuation in part of the co-pending commonly assigned application Ser. No. 657,888, filed Oct. 5, 1984, now U.S. Pat. No. 4,715,261.
It has long been recognized by designers of systems employing chemical explosives for accelerating a projectile through a barrel bore that it is desirable for the pressure acting on the projectile and within the barrel to remain substantially constant while the projectile is accelerated through the bore. The constant pressure is desirable because it provides constant acceleration for a relatively prolonged time interval to the projectile, to increase the total energy applied to the projectile at the time the projectile leaves the barrel muzzle. The constant pressure in the bore also enables the bore strength to be reduced relative to the situation of a pulsed propulsive force. This is because the pulse must have a higher initial force to achieve a muzzle velocity which is attained with a constant pressure source.
Obtaining a constant barrel pressure, however, is difficult because of the constantly increasing volume in the barrel, behind the projectile. Because of the constantly increasing barrel volume, constant pressure can be achieved by adding additional gaseous material to the barrel, as the projectile is being accelerated, or by heating the material in the barrel so that the material becomes more energetic as the projectile is being accelerated through the barrel. The impulsive nature of chemical explosions, however, does not enable either of those results to be achieved. Thus, despite many efforts, chemical explosive devices have been unable to achieve the desirable result of a constant pressure in a barrel, acting on a projectile. A further disadvantage of chemically driven projectile devices is that they are efficient, reliable devices for projectile velocities only below about 1.5 kilometers per second. Because chemical propellants are generally high density exothermic compounds producing two phase mixtures, sound speed limitations thereof cause a rapid decline in energy conversion efficiency for projectile velocities above about 1.5 kilometers per second. In the hypervelocity range, above 1.5 kilometers per second, it is desirable to use other energy sources to conveniently heat packaged low atomic weight propellants inside of a gun.
We have now realized that electrically controlled hypervelocity (more than 1.5 kilometers per second) plasma propulsive systems are capable of providing the desired result of constant pressure acting on a projectile being accelerated through a bore. Electrical sources to energize plasma jets to achieve hypervelocity projectiles are disclosed in the copending, commonly assigned application of Goldstein et al, Ser. No. 471,215, filed Mar. 1, 1983, now U.S. Pat. No. 4,590,842, and our copending application entitled Cartridge Containing Plasma Source for Accelerating a Projectile, Lowe, King, Price & Becker Docket 277-004, Ser. No. 657,888 filed Oct. 5, 1984, now U.S. Pat No. 4,715,261. In the '215 application, a projectile is accelerated along a bore by plural plasma jet sources, located at different longitudinal positions along the length of the bore. The jet sources have an oblique angle with respect to the bore. In our copending application, a projectile is accelerated from a gun having a barrel with a bore adapted to receive the projectile and a breech block having a bore aligned with the barrel bore. A cartridge in the breech block bore responds to an electric source to supply a high temperature, high pressure plasma jet to the rear of the projectile in the bore.
In both of the aforementioned inventions, the plasma jet source includes a tube having an interior wall forming a capillary passage, i.e., a passage having a length to diameter ratio of at least 10:1. A discharge voltage is supplied by a suitable source between spaced regions along the length of the interior wall while a dielectric ionizable substance is between the regions. The dielectric ionizable substance includes at least one element that is ionized to form a plasma in response to the discharge voltage being applied between the spaced regions. The passage has a diametric length that is short relative to the distance between the spaced regions to form the capillary passage. First and second ends of the passage are respectively opened and blocked to enable and prevent the flow of plasma through them. The plasma forms an electric discharge channel between the spaced regions. Ohmic dissipation occurs in the electric discharge channel to produce a high pressure in the passage to cause the plasma in the passage to flow longitudinally in the passage through the first, i.e., open, end to form the plasma jet which accelerates the projectile through the bore.